Method for predicting frictional resistance of rough surface, and apparatus for estimating surface performance
AssigneeChugoku Marine Paints, Ltd.
InventorHirohisa Mieno
Life of this patent
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Abstract
The invention provides a method which predicts a ratio of the increase in frictional resistance of a rough surface in a simple manner, quickly and without variations in predicted results among individuals. The method for predicting the frictional resistance of a rough surface having a variation in roughness wavelength, and being in contact with a fluid flowing at varied velocities includes evaluating the total projected area of all prominent peaks standing out above the viscous sublayer thickness per unit area, and calculating the friction increase ratio FIR (%) or the frictional resistance increase Δτ.
Claims16
A method for predicting frictional resistance of a rough surface having a variation in roughness wavelength and being in contact with a fluid flowing at varied velocities, the method comprising:
- measuring roughness of the rough surface with a surface roughness meter,
- determining a prominent peak projected area A of the rough surface, which is a total projected area of all prominent peaks standing out above a viscous sublayer thickness per unit area, based on the measured roughness of the rough surface;
- and
- calculating a friction increase ratio FIR (%) using Equation (1) or a frictional resistance increase Δτ using Equation (2):
- FIR
-
- (
- %
- )
- =
- C
- ×
- A
- (
- 1
- )
- Δ
-
-
- τ
- =
- C
- r
-
- 1
- 2
-
- ρ
-
-
- AV
- 2
- ,
- (
- 2
- )
- wherein in Equation (1), the coefficient C is a constant dependent on the prominent peak projected area A and is predetermined by performing a frictional resistance test beforehand in which frictional resistances are measured with respect to a plurality of rough surfaces having different degree of roughness while changing a flow velocity V and friction increase ratios FIR (%) of the plurality of rough surfaces are calculated, wherein the friction increase ratios FIR (%) are percentages of differences τr−τ0 between frictional resistances τrof the plurality of rough surfaces and a frictional resistance τ0of a smooth surface, divided by τ0, and
- in Equation (2), the coefficient Cr is a constant dependent on a fluid density ρ, the prominent peak projected area A and the flow velocity V, and is predetermined from the relation of Equation (2) using values of frictional resistance increase Δτ obtained beforehand by a frictional resistance test in which frictional resistances are measured with respect to a plurality of rough surfaces having different degree of roughness while changing a flow velocity V, wherein the values of frictional resistance increase Δτ are differences τr−τ0 between frictional resistances τr of the plurality of rough surfaces and a frictional resistance τ0 of a smooth surface.
A surface performance estimating apparatus for estimating surface performance, comprising:
- a measurement section configured to measure a roughness height R and an average length RSm of roughness curve elements;
- and
- a calculation unit configured to calculate a prominent peak projected area A, which is a total projected area of all prominent peaks standing out above a viscous sublayer thickness per unit area, and to calculate a friction increase ratio FIR (%) using Equation (1) or a frictional resistance increase AT using Equation (2):
- FIR
-
- (
- %
- )
- =
- C
- ×
- A
- (
- 1
- )
- Δ
-
-
- τ
- =
- C
- r
-
- 1
- 2
-
- ρ
-
-
- AV
- 2
- ,
- (
- 2
- )
- wherein in Equation (1), the coefficient C is a constant dependent on the prominent peak projected area A and is predetermined by performing a frictional resistance test beforehand in which frictional resistances are measured with respect to a plurality of rough surfaces having different degree of roughness while changing a flow velocity V and friction increase ratios FIR (%) of the plurality of rough surfaces are calculated, wherein the friction increase ratios FIR (%) are percentages of differences τr−τ0 between frictional resistances τr of the plurality of rough surfaces and a frictional resistance τ0 of a smooth surface, divided by τ0 , and
- in Equation (2), the coefficient Cr is a constant dependent on a fluid density ρ, the prominent peak projected area A and the flow velocity V, and is predetermined from the relation of Equation (2) using values of frictional resistance increase Δτ obtained beforehand by a frictional resistance test in which frictional resistances are measured with respect to a plurality of rough surfaces having different degree of roughness while changing a flow velocity V, wherein the values of frictional resistance increase Δτ are differences τr−τ0 between frictional resistances τr of the plurality of rough surfaces and a frictional resistance τ0 of a smooth surface.
Dependencies are inferred from the claim text.